Display is a process for converting an electric signal (data information) into a visible light (visual information), where an apparatus completing the display is a man-machine Interface (MMI) and flat panel displays (FPD) are a class of display apparatus which are the most popular currently. A liquid crystal display, (LCD) is a product which is the first developed and commercialized in FPDs. Currently, thin film transistor liquid crystals (TFT-LCD) have become a mainstream product in LCD application.
The development of TFT-LCD has experienced a lengthy stage of fundamental research, and after the realization of a mass production and commercialization, the TFT-LCD products have the advantages such as it being light and thin and environmentally friendly, high performance and the like, such that the size gets larger and larger, and the use becomes more and wider. Whether in a small-sized mobile phone screen, or a large-sized notebook computer (PC) or a monitor, and a large-scaled liquid crystal display television (LCDTV), the TFT-LCDs find application. The early commercial TFT-LCD products are essentially of a twisted nematic (TN) display mode, and the greatest problem is a visual angle not big enough. With the increase in size of the TFT-LCD products, particularly the use of the TFT-LCDs in the TV field, an in-plane switching (IPS) display mode featuring a wide view angle has been developed and applied. The IPS display mode is first published in the paper by the American R. Soref in 1974, and the German G Baur proposes to use the IPS as a wide view angle technique in the TFT-LCDs. In 1995, Japanese HITACHI CORPORATION developed the first 13.3-inch wide view angle TFT-LCD product of an IPS mode in the world. Korean Modern Corporation developed a TFT-LCD product of a fringe field switching (FFS) display mode on the basis of IPS.
The TFT-LCD is a liquid crystal display device with a TFT switch control, and the electrical and optical properties of the liquid crystal directly affect the display effect. Different kinds of liquid crystals have different electrical and optical properties, and different display modes. The performance parameters which have greater influences on the liquid crystal materials used in the TFT-LCDs are an operating temperature range, a driving voltage, a response speed, a contrast ratio, a hue, a tone, a view angle, etc., wherein the driving voltage is greatly influenced by the dielectric constant anisotropy and the elastic coefficient, the viscosity and the elastic coefficient affect the response speed of the liquid crystal materials, and the phase difference and the refractive index anisotropy affect the hue of the liquid crystal display. Those previous cyano-containing compounds cannot satisfy these conditions, and only the fluorine-containing liquid crystal materials can be suitable for making TFT-LCDs.
Furthermore, a liquid crystal molecule cannot achieve all the requirements of the TFT-LCD display, so various liquid crystal molecules must be combined. The various physical property requirements of the liquid crystal material can be achieved by combining various liquid crystal molecules, and these requirements mainly comprise 1) a high stability, 2) a moderate birefringence, 3) a low viscosity, 4) a greater dielectric anisotropy, and 5) a wide temperature range. An ideal storage temperature range is −40° C.-100° C., and in general, in a special use such as a vehicle display, the temperature can be expanded to −40° C.-110° C.
Nowadays, the LCD product technique has become very mature, and successfully solves the technical difficulties such as a view angle, a resolution, a color saturation, brightness, etc., and the display performance thereof has been close to or more than that of CRT displays. The large-sized and medium- and small-sized LCDs have gradually become the dominant products of flat panel displays in respective fields. In order to pursue a higher performance specification, accelerating the response time has become an object pursued by various device manufacturers. In particular, the response time of a liquid crystal is restricted by the rotary viscosity γ1/elastic constant K of a liquid crystal, and therefore, in view of a liquid crystal material, it is required to try to find a method to reduce the rotary viscosity γ1 of a liquid crystal medium, and at the same time, to increase the elastic constant K to reach the purpose of accelerating the response time. However, in an actual research, it is found that the rotary viscosity and the elastic constant are a pair of contradictory parameters, and a reduction of the rotary viscosity will results in an increase of the elastic constant, and as a result, the object for reducing the response time cannot be achieved. The object for accelerating the response time can be achieved by reducing a cell thickness d from a device aspect, which would be very easy to achieve; however, since the delay amount Δnd of a device is fixed, it is required to increase the optical anisotropy Δn in view of a liquid crystal material in order to reduce the cell thickness d thereof; therefore, in order to achieve the above-mentioned requirements, it is necessary to develop a series of compounds with superior performances to solve the problem that the response time of a liquid crystal display is slow.